Preparation and characterisation of IAEA‐603, a new primary reference material aimed at the VPDB scale realisation for δ 13 C and δ 18 O determination

Abstract

Rationale NBS19 carbonate, a primary reference material (RM) for the Vienna Pee Dee Belemnite (VPDB) scale realisation introduced in 1987, was exhausted in 2009, and no primary RM was available for several years. This study describes the preparation and characterisation of a new RM, IAEA‐603 (Ca‐carbonate, calcite of marble origin), which shall serve as a new primary RM (replacement for NBS19) or primary calibrator aimed at the highest realisation of the VPDB scale for δ 13 C and δ 18 O values, including the VPDB‐CO 2 δ 18 O scale. Methods IAEA‐603 preparation and characterisation (value transfer) against NBS19 were performed by addressing the major modern technical requirements for the production and characterisation of RMs (ISO Guide 35). IAEA‐603 was produced in a large quantity, and the first batch was sealed into ampoules (0.5 g) to ensure RM integrity during storage; four other batches were sealed for long‐term storage. The most accurate method of CO 2 preparation for isotope mass spectrometry was used, namely carbonate–H 3 PO 4 reaction under controlled conditions. Results The assigned values of δ 13 C = +2.460 ± 0.010‰ and δ 18 O = −2.370 ± 0.040‰ ( k = 1) are based on a large number of analyses (~10 mg aliquots) performed at IAEA and address all the known uncertainty components. For aliquots down to 120 μg, the δ 18 O uncertainty remains unchanged but shall be doubled for δ 13 C. The uncertainty components considered are as follows: (a) material homogeneity (within and between the 5200 ampoules produced), (b) value assignment against NBS19, (c) storage effects and (d) effect of the 17 O correction. Conclusions The new primary RM IAEA‐603 replaces NBS19 in its use as the highest calibrator for the VPDB δ 13 C and δ 18 O scale, including the VPDB‐CO 2 δ 18 O scale. The use of IAEA‐603 will allow laboratories worldwide to establish consistent realisation of the scales for δ 13 C and δ 18 O values and metrological comparability of measurement results for decades. The VPDB scale definition based on NBS19 stays valid.

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